Proximity sensor interface

Abstract

A first measured value is determined which is associated with the proximity of a target to an inductive sensor. A first voltage signal having a first amplitude is generated. The first voltage signal is provided as a driving signal to the inductive sensor. A sensor current signal is received as a return signal output from the inductive sensor. The sensor current signal has an amplitude proportional to a proximity of the target to the inductive sensor. The sensor current signal is converted to a corresponding second voltage signal having a second amplitude. A differential measuring technique is used to determine the first measured value in accordance with relative amplitudes of said first voltage signal and said second voltage signal.

1. A method for determining a first measured value comprising:
 generating a first voltage signal having a first amplitude; 
 providing the first voltage signal as a driving signal to the inductive sensor; 
 receiving a sensor current signal as a return signal output from the inductive sensor, said sensor current signal having an amplitude proportional to a proximity of a target to the inductive sensor; 
 converting said sensor current signal to a corresponding second voltage signal having a second amplitude; and 
 using a differential measuring technique to determine said first measured value, said first measured value being proportional to a ratio of relative amplitudes of said first voltage signal and said second voltage signal, said first measured value being associated with the proximity of the target to the inductive sensor. 
 
   
   
     2. The method of  claim 1 , wherein said first measured value is an admittance value, Y, of the inductive sensor. 
   
   
     3. The method of  claim 1 , further comprising:
 providing a sensor receiver which senses said sensor current signal and converts said sensor current signal to said corresponding second voltage signal. 
 
   
   
     4. The method of  claim 3 , wherein said sensor receiver operates as a transconductance amplifier having a non-inverting input, and said return signal from said inductive sensor is held at a same voltage as said non-inverting input of said sensor receiver. 
   
   
     5. The method of  claim 1 , wherein said first voltage signal is sine wave at a selected frequency. 
   
   
     6. The method of  claim 1 , wherein said driving signal is provided to said inductive sensor on a driving signal line and said return signal is provided from said inductive sensor on a return signal line, said driving signal line and said return signal lines having substantially balanced termination impedances. 
   
   
     7. The method of  claim 1 , further comprising:
 providing a first proximity indicator value in accordance with said first measured value, said proximity indicating the proximity of the target to the inductive sensor. 
 
   
   
     8. The method of  claim 7 , further comprising:
 providing a predetermined set of measurement values having corresponding proximity indicator values; and 
 selecting said first proximity indicator value as one of said corresponding proximity indicator values having an associated predetermined measurement value in accordance with said first measured value. 
 
   
   
     9. The method of  claim 1 , wherein said driving signal and said return signal are transmitted over a shielded twisted pair cable. 
   
   
     10. The method of  claim 1 , wherein said driving signal and said return signal are configured to have a potential value other than zero. 
   
   
     11. The method of  claim 10 , wherein said driving signal and said return signal are configured to half a supply voltage. 
   
   
     12. The method of  claim 10 , wherein if a wire fault occurs in any signal line transmitting said driving signal or said return signal and causes said any signal line to fail to ground, there is failure of said inductive sensor, said failure of said inductive sensor being a trigger event for detecting a failed signal line. 
   
   
     13. A method for determining a first measured value comprising:
 generating a first voltage signal having a first amplitude; 
 providing the first voltage signal as a driving signal to the inductive sensor; 
 receiving a sensor current signal as a return signal output from the inductive sensor, said sensor current signal having an amplitude proportional to a proximity of a target to the inductive sensor; 
 converting said sensor current signal to a corresponding second voltage signal having a second amplitude; and 
 using a differential measuring technique to determine said first measured value in accordance with relative amplitudes of said first voltage signal and said second voltage signal, said first measured value being associated with the proximity of the target to the inductive sensor, wherein said first measured value is an admittance value, Y, of the inductive sensor, and wherein Y is represented as: 
 
     
       
         
           
             Es 
             
               Er 
               * 
               Reference 
             
           
         
       
       and wherein Er is said first amplitude of said first voltage signal, Es is said second amplitude of said second voltage signal and Reference is a known reference value of a component. 
     
   
   
     14. The method of  claim 13 , wherein said component is a reference resistor. 
   
   
     15. The method of  claim 14 , further comprising:
 providing said reference resistor having a resistance value selected in accordance with an impedance of said inductive sensor. 
 
   
   
     16. A method for determining a first measured value comprising:
 generating a first voltage signal having a first amplitude; 
 providing the first voltage signal as a driving signal to the inductive sensor; 
 receiving a sensor current signal as a return signal output from the inductive sensor, said sensor current signal having an amplitude proportional to a proximity of a target to the inductive sensor; 
 converting said sensor current signal to a corresponding second voltage signal having a second amplitude; 
 using a differential measuring technique to determine said first measured value in accordance with relative amplitudes of said first voltage signal and said second voltage signal, said first measured value being associated with the proximity of the target to the inductive sensor; 
 providing a switch that switches between said first voltage signal and said second voltage signal; 
 measuring said first voltage signal to determine said first amplitude when said switch is in a first setting; and 
 measuring said second voltage signal to determine said second amplitude when said switch is in a second different setting, and 
 wherein said driving signal is continuously provided to said inductive sensor while measuring said second voltage signal. 
 
   
   
     17. The method of  claim 16 , wherein said driving signal applied to said inductive sensor has said first amplitude providing a full available excitation voltage, and said driving signal continuously provided to said inductive sensor provides for switching between said second voltage signal and said first voltage signal without incurring a transient settling time associated with reconnecting said inductive sensor to said driving signal. 
   
   
     18. A method for determining a first measured value comprising:
 generating a first voltage signal having a first amplitude; 
 providing the first voltage signal as a driving signal to the inductive sensor; 
 receiving a sensor current signal as a return signal output from the inductive sensor, said sensor current signal having an amplitude proportional to a proximity of a target to the inductive sensor; 
 converting said sensor current signal to a corresponding second voltage signal having a second amplitude; 
 using a differential measuring technique to determine said first measured value in accordance with relative amplitudes of said first voltage signal and said second voltage signal, said first measured value being associated with the proximity of the target to the inductive sensor; and 
 providing a sensor receiver which senses said sensor current signal and converts said sensor current signal to said corresponding second voltage signal, wherein said first measured value is determined using only said relative amplitudes and a known reference value of a single reference component included in said sensor receiver. 
 
   
   
     19. The method of  claim 18 , wherein said single reference component is a resistor through which said sensor current signal flows, said second magnitude of said second voltage signal being proportional to said known reference value and an amplitude of said second current signal. 
   
   
     20. An inductive sensing apparatus for determining a first measured value comprising:
 a sensor driver generating a first voltage signal having a first amplitude; 
 an inductive sensor having the first voltage signal as a driving signal; 
 a sensor receiver receiving a sensor current signal as a return signal output from the inductive sensor, said sensor current signal having an amplitude proportional to a proximity of a target to the inductive sensor, said sensor receiver converting said sensor current signal to a corresponding second voltage signal having a second amplitude; and 
 a component that performs a differential measuring technique to determine said first measured value, said first measured value being proportional to a ratio of relative amplitudes of said first voltage signal and said second voltage signal, said first measured value being associated with the proximity of the target to the inductive sensor. 
 
   
   
     21. The apparatus of  claim 20 , wherein said first measured value is an admittance value, Y, of the inductive sensor. 
   
   
     22. The apparatus of  claim 20 , further comprising:
 a sensor receiver which senses said sensor current signal and converts said sensor current signal to said corresponding second voltage signal. 
 
   
   
     23. The apparatus of  claim 22 , wherein said sensor receiver operates as a transconductance amplifier having a non-inverting input, and said return signal from said inductive sensor is held at a same voltage as said non-inverting input of said sensor receiver. 
   
   
     24. The apparatus of  claim 20 , wherein said first voltage signal is sine wave at a selected frequency. 
   
   
     25. The apparatus of  claim 20 , wherein said driving signal is provided to said inductive sensor on a driving signal line and said return signal is provided from said inductive sensor on a return signal line, said driving signal line and said return signal lines having substantially balanced termination impedances. 
   
   
     26. The apparatus of  claim 20 , wherein a first proximity indicator value is provided in accordance with said first measured value, said proximity indicating the proximity of the target to the inductive sensor. 
   
   
     27. The apparatus of  claim 26 , further comprising:
 a predetermined set of measurement values stored in a memory having corresponding proximity indicator values, wherein said first proximity indicator value is selected as one of said corresponding proximity indicator values having an associated predetermined measurement value in accordance with said first measured value. 
 
   
   
     28. The apparatus of  claim 20 , wherein said driving signal and said return signal are transmitted over a shielded twisted pair cable. 
   
   
     29. The apparatus of  claim 20 , wherein said driving signal and said return signal are configured to have a potential value other than zero. 
   
   
     30. The apparatus of  claim 29 , wherein said driving signal and said return signal are configured to half a supply voltage. 
   
   
     31. The apparatus of  claim 29 , wherein if a wire fault occurs in any signal line transmitting said driving signal or said return signal and causes said any signal line to fail to ground, there is failure of said inductive sensor, said failure of said inductive sensor being a trigger event for detecting a failed signal line. 
   
   
     32. An inductive sensing apparatus for determining a first measured value comprising:
 a sensor driver generating a first voltage signal having a first amplitude; 
 an inductive sensor having the first voltage signal as a driving signal; 
 a sensor receiver receiving a sensor current signal as a return signal output from the inductive sensor, said sensor current signal having an amplitude proportional to a proximity of a target to the inductive sensor, said sensor receiver converting said sensor current signal to a corresponding second voltage signal having a second amplitude; and 
 a component that performs a differential measuring technique to determine said first measured value in accordance with relative amplitudes of said first voltage signal and said second voltage signal, said first measured value being associated with the proximity of the target to the inductive sensor, wherein said first measured value is an admittance value, Y, of the inductive sensor, and wherein Y is represented as: 
 
     
       
         
           
             Es 
             
               Er 
               * 
               Reference 
             
           
         
       
       and wherein Er is said first amplitude of said first voltage signal, Es is said second amplitude of said second voltage signal and Reference is a known reference value of a second component. 
     
   
   
     33. The apparatus of  claim 32 , wherein said second component is a reference resistor. 
   
   
     34. The apparatus of  claim 33 , wherein said reference resistor has a resistance value selected in accordance with an impedance of said inductive sensor. 
   
   
     35. An inductive sensing apparatus for determining a first measured value comprising:
 a sensor driver generating a first voltage signal having a first amplitude; 
 an inductive sensor having the first voltage signal as a driving signal; 
 a sensor receiver receiving a sensor current signal as a return signal output from the inductive sensor, said sensor current signal having an amplitude proportional to a proximity of a target to the inductive sensor, said sensor receiver converting said sensor current signal to a corresponding second voltage signal having a second amplitude; 
 a component that performs a differential measuring technique to determine said first measured value in accordance with relative amplitudes of said first voltage signal and said second voltage signal, said first measured value being associated with the proximity of the target to the inductive sensor; and 
 a switch that switches between said first voltage signal and said second voltage signal, and wherein said first voltage signal is measured to determine said first amplitude when said switch is in a first setting, said second voltage signal is measured to determine said second amplitude when said switch is in a second different setting, and said driving signal is continuously provided to said inductive sensor while measuring said second voltage signal. 
 
   
   
     36. The apparatus of  claim 35 , wherein said driving signal applied to said inductive sensor has said first amplitude providing a full available excitation voltage, and said driving signal continuously provided to said inductive sensor provides for switching between said second voltage signal and said first voltage signal without incurring a transient settling time associated with reconnecting said inductive sensor to said driving signal. 
   
   
     37. An inductive sensing apparatus for determining a first measured value comprising:
 a sensor driver generating a first voltage signal having a first amplitude; 
 an inductive sensor having the first voltage signal as a driving signal; 
 a sensor receiver receiving a sensor current signal as a return signal output from the inductive sensor, said sensor current signal having an amplitude proportional to a proximity of a target to the inductive sensor, said sensor receiver converting said sensor current signal to a corresponding second voltage signal having a second amplitude; 
 a component that performs a differential measuring technique to determine said first measured value in accordance with relative amplitudes of said first voltage signal and said second voltage signal, said first measured value being associated with the proximity of the target to the inductive sensor; and 
 a sensor receiver which senses said sensor current signal and converts said sensor current signal to said corresponding second voltage signal, wherein said first measured value is determined using only said relative amplitudes and a known reference value of a single reference component included in said sensor receiver. 
 
   
   
     38. The apparatus of  claim 37 , wherein said single reference component is a resistor through which said sensor current signal flows, said second magnitude of said second voltage signal being proportional to said known reference value and an amplitude of said second current signal.